How do I solve this equation: 2000= (500 * (0.001/(3.14r^2)) + (0.0008/(3.14r^4), or even x^2+x^3=1100?

My big problem here is I don't kow how to equate powers. eg 2000= 500 ((x^2)^2) + x^4 how do I resolve for x. Or even x^2+x^3=1100. I know what x is as I made up the example but, if I hadn't made it up I suppose I would have to equate the x^2 and x^3 in some way and solve for that. Any help would be appreciated got an exam in 36 hours. thanks.